The san serif font you have at the bottom is gorgeous! I agree though, I think the font at the top is too playful for the topic. Since the bottom text is san serif, maybe consider a serif? Caslon Pro is always good, as is Cambria.
(I also love the Avenir family for san serif fonts.)
Right now, my issue with it is the sizing on the iPhone - it looks squished and fake. Is there any way you can mess with the original image?
I also like the darker background, but it feels too simple for me.
You're working with a great image and I would hang it on my campus - keep going!